Buried conduits are ubiquitously used for carrying various materials, such as water, natural gas, and sewage. A major problem with buried conduits comprised of metal or concrete with metal reinforcements is corrosion. The severity and rate of corrosion is dependent on the type of material comprising the conduit and the environment in which the conduit is buried. Insuring the longevity of buried conduits is an important part of the infrastructure in the United States and the world. Significant costs are involved in design, development, manufacture, and installation of water, gas, and sewage systems. Failure of these systems from conduit corrosion represents appreciable costs.
The longevity of buried conduits depends on several design and installation features, including resistance to corrosion. There are numerous causes of corrosion, such as oxygen replenishment, presence of sulfides, pH of the surrounding soil environment, stray direct electrical current, and microbiologically-influenced corrosion. In the early 1950's, experimentation was conducted using polyethylene film to encase buried conduits in an effort to prevent corrosion. The results showed that a sleeve of polyethylene film could be easily and quickly slipped over a conduit immediately prior to installation and the sleeve was effective in preventing corrosion, even in severely corrosive soils. Because polyethylene is inexpensive compared to other corrosion abatement systems and is easily applied to conduits, it has become the preferred corrosion abatement system relative to buried conduits.
Polyethylene film is very strong and durable, and can withstand the harsh conditions of burial for an indefinite period. For example, polyethylene sleeves that were installed on buried conduits over 35 years ago, when excavated and examined, exhibited the same physical characteristics they had when first installed. Inspections of field installations years later have confirmed that polyethylene sleeves have generally performed as expected, however, there were some instances of unexplained corrosion. Recent research has shown that colonies of bacteria form on the conduit and their secretions can cause severe corrosion, leading to failure of the buried conduit. The colonies of bacteria consists of both aerobic and anaerobic bacteria, and generally comprise slime-forming, acid-producing, sulfate-producing, nitrate-reducing, iron-oxidizing, and iron-reducing bacteria.
Microbiologically-influenced corrosion ("MIC") from anaerobic sulfate-reducing bacteria ("SRBs") was suspected as the most likely cause of the unexplained corrosion events. The anaerobic bacteria from the genera Desulfovibrio (e.g. Desulfovibrio desulfuricans) have been found to be one of the major contributing causes of MIC. However, currently available methods for controlling conduit corrosion do not address microbiologically-influenced corrosion or their application is technically complex and very expensive, or they are not suitable for buried conduits.